Air compressor



Aug. 9, 1938. sis. REDFIELD AIR COMPRESSOR Filed March 17, 1937 mg h INYENTOR v a. EE'DF/ELD I Pmdzmmw ATTORNEY! Patented Aug. 9, 1938 I Snowden B. Redfield,

Bethlehem, Pa., assignor to Fuller Company, Catasauqua, Pa., a. corporation of Delaware Application March 17,

8 Claims.

This invention relates to rotary compressors and vacuum pumps, and more particularly to an apparatus for improving efficiency by reducing air or gas slippage losses between the ends of the rotating element or elements'and the casing or cylinder heads.

The invention has especially to do with modifications and improvements of the apparatus of my Patent No. 1,994,'786. Similarly to that ap paratus, it may be applied with advantage to compressors'and pumps having various types of rotary elements, to maintain substantially constant minimum clearances between the ends of the rotary elementsand adjacent surfaces of the casing, and is of especial utility in its application to compressors and pumps of the multi-vane type. For simplicity in description, the apparatus will be referred to as an air compressor and specifically described in its application to multl-vane compressors.

The rotors of compressors of this type, designed for relatively high discharge pressures, expand longitudinally a. considerably greater distance than the stator casings or cylinders, as the latter are water-cooled to provide for satisfactory efliciencies. As the rotors are driven at high speeds, it is essential that adequate clearances be provided between the ends of the rotor and the inner surfaces of the cylinder heads to prevent actual contact, and consequent burning or welding of the parts. It is common practice to fix a constant clearance at oneend of the rotor, as by supporting the rotor shaft at that end in a thrust bearing, so that as the rotor is heated it expands longitudinally in the direction of the other or expansion end.

The shaft at theexpansion end of the rotor is supported in a plain radial roller bearing, the

" inner race of which is displaced axially as the 40 rotor expands or contracts. The "flxed end" clearance is established principally with relation to the axial play of the thrust bearing plus a running fit, and in machines of average size will be about .004 of an inch. The expansion end clearance is determined with relation to the temperature of the rotor corresponding to the highest expected operating pressure, the largest volume and lowest temperature of the cooling water and the maximum duration of continuous loading. Under the less extreme conditions of normal operation, the expansion end clearance is excessive and the increasing air slippage is detrimental to efliciency.

In general, the present apparatus has among its purposes to overcome the difficulties described 1937, Serial No. 131,305

above, and comprises a compressor preferably having one end of the rotor fixed against substantial axial movement, with a predetermined minimum safe running clearance, and a movable or floating, internal cylinder head at the expansion end of the rotor, the floating head clearing the surface of the rotor by at least the distance of a running fit. This floating head is of simplified and less costly design and is provided with a bearing surface located so as to provide a positive seal against air slippage around or along the rotor shaft. The bearingsurface is lightly held against an annular'shoulder, on the end of the rotor surrounding the shaft, preferably by air pressure on the outer surface of the floating head slightly above the average pressure on its inner surface. As the rotor expands longitudinally, the floating head is moved axially by the force of the shoulder against the bearing surface. The head is provided with a rearwardly extending sleeve surrounding the shaft, and preferably having an inner surface of bearing metal, the sleeve preventing angular displacement of the head due to the unequal pressures on its inner surface. A rotating collar on the shaft serves to return the head when the rotor contracts, by bearing against the end of the sleeve.

It will be seen, as the description proceeds, that, floating heads of similar design may be used at each end of the rotor, whereby the rotor and floating heads may float axially in either direction until contact is made with one fixed head. This duplication does not materially increase the operating advantages, and as it is more costly than the arrangement described, thelatter is preferred.

For a better understanding of the invention,

reference is made to the accompanying drawing,

in which:

Fig. 1 is a cross-sectional elevation of the compressor, and

Fig. 2 is a cross-section, on a reduced scale, with the vanes shown in their normal running positions.

Referring to the drawing, the apparatus will be seen to consist of a stator casing or cylinder I, having an intake port 2, a discharge port 3, and a generally cylindrical bore 4. The bore is preferably counter-bored and broached at 5, and as shown by the arrows, between the intake and discharge ports, to minimize air slippage, the counter-bore being concentric to a cylindrical rotor 6, arranged eccentrically within the bore 4,

' the rotor being provided with a plurality of preferably radial, equally spaced slots I, the depths of which are indicated by the dotted lines 8, in which vanes or blades 9 are arranged to move outwardly and into contact with the inner wall of the cylinder, due to the effect of centrifugal force.

The rotor is carried by trunnion shafts l0 and H in hearings, to be described in detail hereinafter, in cylinder heads l2 and It. The cylinder is provided with water-jackets H which communicate, as at I5 and IS, with water-jackets in the cylinder heads'l2 and I3, and it will be evident that this arrangement provides for adequate cooling of the stationary parts and that the longitudinal expansion of the cylinder will be relatively less than the uncooled rotor. The fixed end" of therotor is carried by'the cylinder head H, the head having a smooth inner face or surface I1 and a bore l8 through which the shaft H) extends. The fixed end is also preferably the driven and of the rotor, so that accidental thrust due to the driving mechanism may be absorbed in the thrust bearing to be described hereinafter, and the shaft In is accordingly further extended through a packing gland IS in a bearing cover 20, the shaftbeing provided with a key-seat 2| for the usual flexible coupling (not shown). The head I2 is provided with a chamber 22 to receive the outer race of a radial and thrust bearing 23, which is preferably of the roller type, one edge of this race abutting one or more shims 24 which fix the axial pofltion of the bearing, the race being secured by the bearing cover 20. The inner race abuts a shoulder 25 on the shaft I 0, the race being secured to the shaft by a lock-washer and nut 26 threaded thereon and which bear against the retaining ring 21. The number and thickness of the shims 24. in fixing the axial position of the bearing, accordingly fix the clearance between the end of the rotor and the surface I! of the head l2. The bore I8 is sealed against substantial air slippage by a split hub-collar 28, secured to the shaft by a continuous ring and garter spring 29, between the inner race and the end of the rotor.

The p nsion end of the compressor consists of the fixed head I, the head having an eccentric bore of two diameters, that of the larger diameter forming a chamber to receive the outer race 3|! of a plain radial roller bearing II, the outer race being secured in the chamber by fingers II in the bearing cover 32. The inner race 28 abuts a shoulder 34 on the shaft II and is secured by a lock-washer and nut 35 threaded to the shaft. As the rotor expands or contracts, the race 33 is displaced axially. without damage to the bearing Beyond the end of rotor 8, the cylinder is provided with a shallow cylindrical bore 36 to accommodate the disc-shaped floating head 31, the

' bore having a diameter slightly greater than that of bore 4 to extend beyond the bottom of the counter-bore 5. It will be understood that in compressors having a true cylindrical bore, the

bore 28 is unnecessary.

:fitted in the bore 36,

being sealed against air slippa e by sealing rings The floating head 31 consists of a disc loosely the periphery of the disc ll, preferably piston rings of the snap type such as those used in internal combustion engines, but ordinary packing has been found to be satisfactory. The head is provided with a rearwardly extending sleeve ll loosely fitted in the bore of cylinder head ll, the sleeve surrounding shaft and being lined with hearing metal, such as babbitt, as indicated at 40, to form a sleeve bearing for the shaft to prevent scoring of the parts. It is to be understood; however, that the bearing surface 40 is not subjected to substantial radial loading, as suflicient clearance is provided between the sleeve and the bore of head I3 to permit substantial radial displacement, whereby the actual radial load of the rotor is carried by roller bearing 3|. The inner surface of the head 31 is recessed to receive an annular bearing surface 4| preferably of babbitt, surrounding and adjacent to shaft II, the bearing surface 4| abutting va shoulder 42 forming a complementary bearing surface on the end of the rotor below the bottom of the vane-slots, as indicated by the dotted lines 8 the contact of the bearing surface 4| and that of shoulder 42 serving as an effective seal to prevent air slippa e around and along shaft The sealing effect is improved by the admission of lubricating oil through a duct 43 which opens intothe bore through the bearing surface 42.

As the sleeve 39 is eccentric to the head 31, a dowel 44 is provided to prevent partial rotation and consequent jamming against the wall of bore 36. The head 31 is provided with a hole 45 to communicate pressure from the cylinder to the outer surface of the disc. The hole 45 is located so as to communicate pressure slightly above the average pressure of the cylinder, whereby the floating head is pressed toward the rotor and the bearing surface 43 lightly held against the surface of shoulder 42. The outer end of sleeve 29 coincides with a shoulder 46 on shaft II, the sleeve being secured for inward movement, as the rotor contracts, by a lock-washer and nut 41 threaded to the shaft and which bear against a rotating collar 48;

The operation of the apparatus 'will be appar- I ent from the foregoing, and it will be understood that the floating head 31 is freely displaced axially as the rotor expands, and that the bearing surface 42 is not subjected to substantial wear as the thrust necessary to move the head does not exceed substantially that represented by the slightly increased air pressure on its outer surface.

I claim:

1. A rotary compressor comprising the combination of a stator casing, having a central bore and an' air intake and a discharge port communicating therewith, a rotor within the bore having shafts mounted in bearings in fixed heads closing the casing at each end of the bore, said bearings supporting the entire radial load of the rotor, the casing having a length greater than that of the rotor, at least one floating head within the bore between an end of the rotor and the adjacent fixed head, the floating head having a bore through which the rotor shaft passes, annular fiat sealing and thrust bearing surfaces on the rotor and floating head near and encircling the shaft, the annular bearing surfaces being in contact in a plane perpendicular thereto and separating said head and rotor at least the distance of a running fit, said head being provided with a hole opening into the bore of the casing at a location where the pressure on its inner surface is slightly above the average to apply pressure to its outer surface to maintain the annular bearing surfaces in contact as the rotor expands longitudinally, and means secured to the shaft beyond and engaging the floating head to force said head inwardly when the rotor contracts.

2. A rotary compressor comprising the combination of a stator casing, having a central bore and an air intake and a discharge port communicating therewith, a rotor within the bore having shafts mounted in bearings in fixed heads closing the casing at each end of the bore, said bearings supporting the entire radial load of the that of the rotor, at least one floating head with-' in the bore between an end of the rotor and the adjacent fixed head, the floating head having a bore through which the rotor shaft passes, means to separate said head and rotor at least the distance of a running fit comprising an annular flat sealing andthrust bearing surface on the end of the rotor near and surrounding the shaft, a complementary sealing and thrust bearing, surface on the inner surface of the floating head and surrounding its bore, said annular flat bearing surfaces being in contact in a plane perpendicular to the shaft, the floating head being provided with an oil duct opening into the bore of the casing through its annular bearing surface, and

means to apply pressure to the outer surface of said head to maintain said annular bearing surfaces in contact.

'3. A rotary compressor comprising the combination of a stator casing, having a central bore and an air intake and a discharge port com--.

' municating therewith, a rotor within the bore having shafts mounted in bearings in fixed heads closing the casing ateach end of the bore, said bearings supporting the entire radial load of the rotor, the casing having a length greater than that of the 'rotor, at least one floating head within the bore between an end of the rotor and the adjacent fixed head, the floating head having a bore through which the rotor shaft passes. means to separate said head and rotor at least the distance of a running fit comprising an annular shoulder forming a flat sealing and thrust bearing surface carrying no radial load, saidv shoulder being on the end of the rotor near and surrounding the shaft, a complementary sealing and thrust bearing surface of bearing metal secured in a recess provided in the inner surface of the floating head and surrounding its bore, said annular surfaces being ina plane perpendicular to the shaft, means to apply pressure to the outer surface of the floating head to maintain its annular bearing surface in contact with the flat surface of said annular shoulder, and means secured to the shaft beyond and engaging the floating head to force said head inwardly when the rotor contracts.

4. A rotary compressor comprising the combination of a stator casing, having a central bore and an air intake and a discharge port communicating therewith, a rotor within the bore having shafts mounted in bearings in fixed heads closing the casing at each end of the bore, said bearings supporting the entire radial load of the rotor, the casing having a length greater than that of the rotor, the rotor being provided with vane-slots extending throughout its length, at least one floating head within the bore between an end of the rotor and the adjacent fixed head,

the floating head having a bore through which the shaft passes, the rotor being provided with an annularshoulder having a flat sealing and thrust bearing surface surrounding the shaft below the bottoms of the vane-slots to separate the rotor and floating head at least the distance of a running flt, said thrust bearing surface being in a plane perpendicular to the shaft, a comple mentary sealingand thrust bearing surface of bearing metal in a recess provided in and secured to-the inner surface of the floating head and surrounding its bore, means secured to the shaft beyond and-engaging the floating head to force said head inwardly when the rotor contracts and means to apply pressure to the outer annular bearing surface in contact with the annular surface of said shoulder.

5. A rotary compressor comprising the combination of a stator casing, having a central bore and an air intake and a discharge port communicating therewith, a rotor within the bore having shafts mounted in bearingsin fixed heads closing the casing at each end of the bore, said bearings supporting the entire radial load of the rotor, the casing having a length greater than that of the rotor, at least one floating head within the bore between an end of the rotor and the adjacent fixed head, said fixed head having a bore concentric to the shaft, the floating head having a sleeve extending rearwardly into said head bore and surrounding the shaft to prevent angular displacement of the floating head, means to separate the rotor and floating head at least the distance of a running fit comprising annular flat sealing and thrust bearing surfaces on the rotor and floating head near and encircling the shaft, the annular bearing surfaces being in contact in a plane perpendicular to the shaft, means to apply pressure against the outer surface of the floating head to maintain said annular surfaces in contact and means secured to the shaft and bearing against the end of the sleeve to move the floating head inwardly as the rotor contracts.

6. A. rotary compressor comprising the combination of a stator casing, having a central bore and an air intake and a discharge port communicating therewith, a rotor within the bore havin shafts mounted in hearings in flxed heads closing the casing at each end of the bore, said bearings supporting the entire radial load of the rotor, the casing having a length greater than that of the rotor, at least one floating head within the bore between an end of the rotor and the adjacent fixed head, said fixed head having a bore concentric to the shaft, the floating head having a sleeve extending rearwardly into the head bore, the sleeve being lined with hearing metal to form a sleeve bearing for the shaft to prevent angular displacement of the floating head, means to separate the rotor and floating head at least the distance of a running-flt comprising an annular flat sealing and thrust bearing surface on the end of the rotor near and surrounding the shaft, the floating head being provided with an annular recess in its inner surface, a flat annular surface of bearing metal in the recess and complementary to the annular bearing surface on the rotor, means secured to the shaft and bearing against the sleeve to force the floating head inwardly when the rotor contracts and means to communicate air pressure slightly above the average on the inner surface of the floating head between it and the flxed head to hold said annular surfaces in contact.

7. A rotary compressor comprising the combination of a stator casing, having a central bore and an air intake and a discharge port communi cating therewith, a rotor. within the bore having shafts mounted in bearings in flxed heads closing the casing at each end of the bore, said bearings supporting the entire radial load of the rotor, the casing having a length greater than that of the rotor, at least one floating head within the bore between an end of the rotor and the adjacent fixed head, the floating. head comprising a disc loosely fitted in the bore, air sealing means for the periphery'of the disc, the disc being provided with a rearwardly extending sleeve lined with bearing metal and forming a sleeve bearing for the shaft to prevent angular displacement of the disc, the

surrounding the shaft, said shoulder having a flat annular sealing and thrust bearing surface complementary to the annular surface on the floating head, said annular surfaces being in contact in a plane perpendicular to the shaft, and means to apply pressure to the outer surface of the disc to maintain the annular bearing surfaces in contact.

8. A rotary compressor comprising the combination of a stator casing, having a central bore and an air intake and a discharge port communicating therewith, a rotor within the bore having shafts mounted in hearings in fixed heads closing the casing at each end of the bore, the casing having a length greater than that of the rotor, at least one floating head within the bore between an end of the bore and the adjacent fixed head, the floating head comprising a disc. loosely fitted in the bore, air sealing means for the periphery of the disc, the disc being provided with a rearwardly extending sleeve lined with bearing metal and forming a sleeve bearing for the shaft to prevent angular displacement of the disc, the lastnamed fixed head being provided with a bore to receive the sleeve with sufilcient looseness to avoid supporting the radial load of the rotor upon the sleeve bearing surface, the inner surface of the disc being provided with an annular fiat bearing surface of bearing metal near and surrounding the shaft, a shoulder on the end of the rotor surrounding the shaft and forming a complementary bearing surface, said bearing surfaces being in a plane perpendicular to the shaft, means to communicate air pressure above theaverage on the inner surface of the floating head to the space behind the head to hold said bearing surfaces in contact, means secured to the shaft and bearing against the sleeve to force the disc inwardly when the rotor contracts, and an antifriction radial bearing supporting the shaft beyond said means.

SNOWDEN B. REDFIELD. 

